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981.
R.N. Hey F. Martinez S. Diniega D.F. Naar J. Francheteau R. Armijo M. Constantin J.P. Cogné J. Girardeau R. Hekinian R. Searle 《Marine Geophysical Researches》2002,23(1):1-12
Several mechanisms have been proposed to account for the rotation of the nearly north-south abyssal hill fabric formed on the East Pacific Rise north of the Easter Microplate to the nearly east-west trends in the northern microplate interior. Proposed mechanisms include rigid microplate rotation, transform fault – parallel shear, and bookshelf faulting during the transfer of lithosphere from the Nazca Plate to the microplate. We used a submersible magnetometer on a NAUTILE dive program to measure the magnetic vector rotation of a pillow basalt and dike spur near Pito Deep, the present location of the tip of the propagating rift system that created the microplate. Our results, although too limited to draw strong conclusions from, suggest clockwise rotations of the seafloor magnetic vectors inconsistent with the transform-parallel shear model, and larger than can be explained solely by rigid microplate rotation. 相似文献
982.
The basic properties of the dynamic model of a turbulent jet formed by a deep-water sewage discharge into the stratified environment of coastal regions are considered. The model developed was used to estimate the parameters of a floating-up jet of deep wastewater discharge from Sand Island into the basin of Mamala Bay (Hawaii) depending on the season and discharge operation mode. The estimates of the float-up depths of the jet and the initial dilution of the jet were estimated on the basis of model calculations using experimental data on the vertical profiles of the water temperature and salinity under the actual conditions of stratification in the study region. It is shown that the further propagation of the wastewater jet depends on tidal events and internal waves generated by tides. The appearance of turbulent jets at the sea surface was recorded. The model estimates of the parameters of the wastewater discharge were compared with the results of experimental measurements. Good agreement was found, which indicates that the physical mechanisms of the propagation of turbulent jets in a stratified medium are adequately described by the model. 相似文献
983.
Problems with biogenic silica measurement in marginal seas 总被引:5,自引:0,他引:5
Surface sediment samples from the Bohai, Yellow Sea, and the Pacific were used to assess biogenic silica (BSi) content and to study uncertainties in BSi measurements. The contents of BSi in the Bohai and Yellow Sea are all less than 1%. The dissolution of BSi in sediments from the Bohai and Yellow Sea is very important to maintain high levels of silicate in the water column. The non-biogenic silica from clay minerals has an obvious effect on BSi of sediment samples in the Bohai and Yellow Sea with low BSi and high clay minerals. The solid to solution ratio was found to have a great influence on BSi measurement, which can induce uncertainties up to 75%. The effect of loss by sorption and centrifugation is negligible. Interlaboratory comparison of techniques for BSi measurement by the wet alkaline extraction technique of Mortlock and Froelich [Deep-Sea Res. 36 (1989) 1415-1426] with clay correction was suggested to give no significant differences. However, differences in sediment compositions and reagent to sample ratio may limit the application of the wet alkaline extraction method. 相似文献
984.
Baraza J. Ercilla G. Farrán M. Casamor J. L. Sorribas J. Flores J. A. Sierro F. Wersteeg W. 《Marine Geophysical Researches》1997,19(2):115-135
Multibeam bathymetric and ultra high-resolution seismic data reveal that the distal course of the Equatorial Atlantic Mid-Ocean Channel (EAMOC) extends further east and south than was previously known, and is controlled by the presence of morphologic highs related to the Fernando de Noronha Fracture Zone. Distal course of the EAMOC is buried by sediments, and does not have bathymetric expression on the seafloor. The channel fill consists of three seismic sequences, suggesting that the recent geological evolution of the channel is composed of successive phases of decreasing sedimentary activity that finally resulted in its complete burial. Tectonic and volcanic activity related to the Fernando de Noronha Fracture Zone and Ridge, together with the effect of strong pulses of the Antarctic bottom water current during the upper Pliocene are suggested to have contributed to the progressive burial and the final abandonment of the EAMOC. 相似文献
985.
Abstract. Six macrobenthic assemblages of the circalittoral zone found in Strymonikos Gulf, North Aegean Sea, are described and compared with the corresponding ones from other Mediterranean and Atlantic areas. For the delimination of these assemblages and the evaluation of the major environmental gradients governing their distribution, several numerical techniques were used. 相似文献
986.
A geomorphological and statistical analysis of slope canyons from the northern KwaZulu-Natal continental margin is documented
and compared with submarine canyons from the Atlantic margin of the USA. The northern KwaZulu-Natal margin is characterized
by increasing upslope relief, concave slope-gradient profiles and features related to upslope growth of the canyon forms.
Discounting slope-gradient profile, this morphology is strikingly similar to canyon systems of the New Jersey slope. Several
phases of canyon incision indicate that downslope erosion is also an important factor in the evolution of the northern KwaZulu-Natal
canyon systems. Despite the strong similarities between the northern KwaZulu-Natal and New Jersey slope-canyon systems, key
differences are evident: (1) the concavity of the northern KwaZulu-Natal slope, contrasting with the ∼linear New Jersey slope;
(2) the relative isolation of the northern KwaZulu-Natal canyons, rather than the dense clustering of the New Jersey canyons;
and (3) the absence of strongly shelf-breaching canyons along the northern KwaZulu-Natal margin. In comparison with the New
Jersey margin, we surmise a more youthful stage of canyon evolution, a result of either the canyons themselves being younger
or the formative processes being less active. Less complicated patterns of erosion resulting from reduced sediment availability
have developed in northern KwaZulu-Natal. The reduction in slope concavity on the New Jersey margin may be the result of grading
of the upper slope by intensive headward erosion, a process more subdued—or less evident—on the KwaZulu-Natal margin. 相似文献
987.
Among the assumptions upon which linear time-invariant models of floating bodies are based is that the body motions are so small that any change in the body’s angular position can be disregarded. However, it is often a major design requirement of a wave energy conversion device that the response amplitude is large, thereby invalidating one of the assumptions of the linear model. In particular, the immersed geometry of a body undergoes considerable variation when it is moved in pitch. With regard to this we investigate the difference in performance between a quasi-linear model in which the change of immersed surface is modelled by time-varying parameters and a basic linear model in which the immersed surface is time-invariant. The time-varying parameter model is realized by interpolation between the appropriate parameter values of a set of linear time-invariant (LTI) models derived for the different immersed surfaces that occur at discrete body displacements. It is shown that the responses predicted using the time-varying parameter model are closer to those measured experimentally than those of a standard frequency-domain model. Particular improvement occurs when the responses are large, such as at or near the resonance frequency. A problem which may limit the general use of the model is also discussed. 相似文献
988.
989.
A complexometric titration technique was employed to measure the total capacity of a variety of marine organisms to adsorb Cu2+. Measured adsorption capacities were 0.22 meq g−1 for phytoplankton, 0.3–1.0 meq g−1 for macrophytes, 1.0–2.5 meq g−1 for zooplankton and 0.3 meq g−1 for suspended particulate matter. The capacity of these materials to adsorb Cu2+ was reduced significantly in the presence of Mg2+ at seawater concentrations. Competition between Mgt2+ and Cu2+ for adsorption sites at pH 6 is described by an average conditional equilibrium constant of 103.7. This constant is such that very little Cu2+ may be adsorbed onto particulates and marine phytoplankton in the presence of Mg2+. Further, primary productivity data and estimates of the detrital carbon sedimentation in Long Island Sound suggest that the flux of particulate carbon is insufficient to remove significant amounts of Cu from the water column to sediments by adsorption mechanisms. 相似文献
990.